The Optimal Cosmic Epoch for Precision Cosmology

TL;DR

This paper identifies the optimal cosmic epoch, around redshift 10, for precision measurements of primordial density perturbations, emphasizing the limitations of future observations due to the diminishing number of accessible regions.

Contribution

It demonstrates that the best constraints on initial density perturbations occur at redshift ~10, highlighting the temporal window for optimal cosmological observations.

Findings

Optimal epoch for measurements is around redshift 10.

Constraints deteriorate rapidly in the future.

Number of accessible regions decreases over cosmic time.

Abstract

The statistical uncertainty in measuring the primordial density perturbations on a given comoving scale is dictated by the number of independent regions of that scale that are accessible to an observer. This number varies with cosmic time and diminishes per Hubble volume in the distant past or future of the standard cosmological model. We show that the best constraints on the initial power spectrum of linear density perturbations are accessible (e.g. through 21-cm intensity mapping) at redshifts z~10, and that the ability to constrain the cosmological initial conditions will deteriorate quickly in our cosmic future.